Typically, an imaging device using a photoelectric layer in combination with an array of field emission type electron sources employs passive matrix activation or active matrix activation. In certain known active matrix activation methods, a particular electron source is activated through the use of two lines, a column selection line (e.g., from a column scanning driver) and a row selection line (e.g. from a row scanning driver), where of one of signal lines also serves as the voltage source to provide power to the selected electron source. In the case of field emission type electron source arrays employing such an activation system, the selection/voltage source line requires the capability of handling a voltage of tens of volts. When such high voltages are used in a signal selection circuit, the consumption of electric power due to the switching activity becomes extremely high, because the level of electric consumption is a function of a square of the voltage. Further, when the voltage in the signal line is large, the ability of the switching circuit to operate under a fast response time is adversely affected due to distortion of the voltage waveform.
In certain hold-type display devices using active matrix activation, the voltage source is separate from the two selection lines (column and row). That is, a particular electron source is activated through the activation of a first signal line and a second signal line, in addition to the voltage for activating the electron source being provided through a third voltage supply line. Typically, one of the two signal lines provides signals of varying voltages to control the length of electron source activation and thus the level of total electron emission (e.g., to control the pixel display intensity). Consequently, the voltage of the signal line carrying the pixel intensity signal may be large, e.g., 15 volts, which results in high energy consumption and a degradation of the response time capability of the switching circuit. Further, the switching time of the activation transistor is limited by the charging time and the charging capacity of the associated capacitor. For these reasons, such systems are not well suited for high speed operations such as dot by dot (or line by line) sequential activation.
Further, X-rays are a form of electromagnetic radiation, which are typically generated by an x-ray generator. An x-ray generator is a device used to generate x-rays, typically used in radiography to acquire an x-ray image representing the inside of an object enabling imaging of the human body for diagnosis or treating medical problems, for example. X-ray technology may further be used, apart from medicine, in fields such as non-destructive testing, sterilization, florescence and the like.
X-ray tubes, typically comprise a cathode assembly configured to emit electrons into the vacuum and an anode assembly configured to collect the electrons and the tube housing, thus establishing a flow of electrical current, known as the electron beam, through the tube. A high voltage power source is connected across the cathode and the anode to accelerate the electrons, striking the target at high speed after being accelerated. The electron beam is focused and strikes the anode target at a focal spot. Thus, electrons from the cathode collide with the anode material, such as tungsten, molybdenum or copper, and accelerate other electrons, ions and nuclei within the anode material. About 1% of the energy generated is emitted/radiated, usually perpendicular to the path of the electron beam, as x-rays. The rest of the energy is released as heat.
It is particularly noted that a typical x-ray source has a filament type hot cathode for its emitter, which is heated by an electric current passing through the filament. Another type of cathode that is not electrically heated by a filament is a cold cathode, which may be used as a replacement for the hot cathode. However cold cathode x-ray sources lack robustness in high voltage applications.
In high voltage applications using an emitter such as an x-ray source, some of the (de)gas molecules from the anode are ionized and accelerated in a beam of ions towards the emitting cathode. This beam can cause severe damage to the emitters due to the high energy ion bombardment.
There is a need for a robust cold cathode resilient to such ion bombardments in high voltage applications. The current disclosure addresses this need.